Heavy metals can be present in trace amounts in all types of produced fluids such as natural gases and crude oils. The amount can range from below the analytical detection limit to several thousand ppbw (parts per billion by weight) depending on the source. In the case of natural gas and natural gas liquids, it is likely to be present as elemental mercury; whilst in crude oil it may also be present as mercuric sulfide (metacinnabar) and or organo-metallic and ionic mercury.
Methods have been disclosed to remove heavy metals such as mercury from produced fluids. US Patent Publication No. 2011/0253375 discloses an apparatus and related methods for removing mercury from reservoir effluent by placing materials designed to adsorb mercury into the vicinity of a formation at a downhole location, and letting the reservoir effluent flow through the volume of the adsorbing material. US Patent Publication No. 2012/0073811 discloses a method for mercury removal by injecting a solid sorbent into a wellbore intersecting a subterranean reservoir containing hydrocarbon products.
Other common approaches utilize treatments for the fluids once the fluids are recovered from subterranean reservoirs and brought to a surface production installation. U.S. Pat. No. 4,551,237 discloses the use of an aqueous solution of sulfide materials to remove arsenic from oil shale. U.S. Pat. No. 4,877,515 discloses a process for removing mercury from hydrocarbon streams, gas or liquid. U.S. Pat. No. 4,915,818 discloses a method of removing mercury from liquid hydrocarbons (natural gas condensate) by contact with a dilute aqueous solution of alkali metal sulfide salt. U.S. Pat. No. 6,268,543 discloses a method for removing elemental mercury with a sulfur compound. U.S. Pat. No. 6,350,372 discloses removing mercury from a hydrocarbon feed by contact with an oil soluble or oil miscible sulfur compound U.S. Pat. No. 4,474,896 discloses using polysulfide based absorbents to remove elemental mercury) (Hg0) from gaseous and liquid hydrocarbon streams.
There is still a need for improved methods and systems to remove heavy metals, particularly mercury, from fluids such as natural gas and upstream from the processing plant if possible.